In Dept. of Transp. v. Adams 193 Ga. App. 866-867 (1) (389 SE2d 343) (1989), the condemnees' expert testified that in arriving at his opinion as to value, he had used a sale occurring over one year after the condemnation as a comparable sale. The condemnor sought to impeach the expert by showing that the same property had been sold only a few months after the condemnation. The condemnees argued that any error in the trial court's refusal to allow the impeachment was harmless because the jury had returned a verdict in an amount less than the opinion given by the expert at trial. Adams rejected the condemnees' "harmless error" argument, recognizing that if the expert had been impeached, the jury would have been authorized to discount the entirety of his testimony. Therefore, even though the verdict may have been lower than the expert's opinion as to value, it could not be said with any certainty that the verdict would not have been even lower had he been impeached.